演练5-1：Contoso大学校园管理1

**演练目的：掌握复杂模型的应用程序开发。

      Contoso大学校园管理系统功能包括学生、课程、教师的管理。

一、创建MVC Web应用程序

      显示效果如下图，操作步骤略。

二、创建数据模型

1.创建学生实体

using System;
using System.Collections.Generic;

namespace ContosoUniversity.Models
{
    public class Student
    {
        public int StudentID { get; set; }
        public string LastName { get; set; }
        public string FirstMidName { get; set; }
        public DateTime EnrollmentDate { get; set; }
        
        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}

      StudentID属性时主键，EF默认将Id或者classnameID作为主键。

      Enrollments属性是导航属性，导航属性拥有与这个实体相关联的实体。此处为学生实体拥有相关的所有课程注册实体，如在数据库中，课程注册表中张三有三条记录，那么导航属性就会有3条Enrollment行。创建导航属性后，数据库数据表将自动生成外键。如果导航属性能包含多个实体（如一对多，多对多），类型必须为集合，比如Icollection。

      导航属性通常定义成virtual，这样就可以好好利用EF的lazy loading（延迟加载）功能。延迟加载是指暂时不需要该数据，不用在当前马上加载，而可以推迟到使用它时再加载。延迟加载是一种很重要的数据访问特性，可以有效地减少与数据源的交互（注意，这里所提的交互不是指交互次数，而是指交互的数据量），从而提升程序性能。

2.创建课程实体

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;

namespace ContosoUniversity.Models
{
    public class Course
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int CourseID { get; set; }
        public string Title { get; set; }
        public int Credits { get; set; }
        
        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}

      Enrollments属性是导航属性。

      CourseID考虑到可能有特殊的数据规则，使用[DatabaseGenerated(DatabaseGeneratedOption.None)]，将不采用数据库自动生成的序号。

3.创建注册实体

namespace ContosoUniversity.Models
{
    public enum Grade
    {
        A, B, C, D, F
    }

    public class Enrollment
    {
        public int EnrollmentID { get; set; }
        public int CourseID { get; set; }
        public int StudentID { get; set; }
        public Grade? Grade { get; set; }
        
        public virtual Course Course { get; set; }
        public virtual Student Student { get; set; }
    }
}

      Grade属性是一个enum枚举类型，?表示该属性可以为空。

      StudentID属性是一个外键，相应的导航属性是Student。一个注册实体和一个学生实体相关联，所以导航属性拥有一个Student实体，而不是之前的ICollection集合。

      CourseID同理。

4.创建数据库上下文

      创建一个DAL（Data Access Layer）文件夹，在文件夹中新建SchoolContext.cs类。

using ContosoUniversity.Models;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;

namespace ContosoUniversity.DAL
{
    public class SchoolContext : DbContext
    {
        public DbSet<Student> Students { get; set; }
        public DbSet<Enrollment> Enrollments { get; set; }
        public DbSet<Course> Courses { get; set; }
    }
}

      这段代码为每个实体集合，创建了一个DbSet属性。在EF技术中，一个实体集合对应一张数据库表，一个实体对应表中的一行。

      修改Web.config文件。

<add name="SchoolContext" connectionString="Data Source=(LocalDb)v11.0;Initial Catalog=ContosoUniversity;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|ContosoUniversity.mdf" providerName="System.Data.SqlClient" />

      默认情况下，EF会寻找DbContext类名字的连接字符串名字。在这个连接字符串中，你已经在App_Data文件夹下添加了一个名字为ContosoUniversity.mdf的LocalDB数据库。如果没有指定连接字符串，EF会为你新建一个。
5.开启Code First Migrations

（1）打开Package Manager控制台

（2）输入命令Enable-Migrations -ContextTypeName SchoolContext

    Configuration类包含一个Seed方法，可以在数据库创建时插入一些模型数据，作为测试数据。

namespace ContosoUniversity.Migrations
{
   using System;
   using System.Collections.Generic;
   using System.Data.Entity.Migrations;
   using System.Linq;
   using ContosoUniversity.Models;

   internal sealed class Configuration : DbMigrationsConfiguration<ContosoUniversity.DAL.SchoolContext>
   {
      public Configuration()
      {
         AutomaticMigrationsEnabled = false;
      }

      protected override void Seed(ContosoUniversity.DAL.SchoolContext context)
      {
         var students = new List<Student>
            {
                new Student { FirstMidName = "Carson",   LastName = "Alexander", 
                    EnrollmentDate = DateTime.Parse("2010-09-01") },
                new Student { FirstMidName = "Meredith", LastName = "Alonso",    
                    EnrollmentDate = DateTime.Parse("2012-09-01") },
                new Student { FirstMidName = "Arturo",   LastName = "Anand",     
                    EnrollmentDate = DateTime.Parse("2013-09-01") },
                new Student { FirstMidName = "Gytis",    LastName = "Barzdukas", 
                    EnrollmentDate = DateTime.Parse("2012-09-01") },
                new Student { FirstMidName = "Yan",      LastName = "Li",        
                    EnrollmentDate = DateTime.Parse("2012-09-01") },
                new Student { FirstMidName = "Peggy",    LastName = "Justice",   
                    EnrollmentDate = DateTime.Parse("2011-09-01") },
                new Student { FirstMidName = "Laura",    LastName = "Norman",    
                    EnrollmentDate = DateTime.Parse("2013-09-01") },
                new Student { FirstMidName = "Nino",     LastName = "Olivetto",  
                    EnrollmentDate = DateTime.Parse("2005-08-11") }
            };
         students.ForEach(s => context.Students.AddOrUpdate(p => p.LastName, s));
         context.SaveChanges();

         var courses = new List<Course>
            {
                new Course {CourseID = 1050, Title = "Chemistry",      Credits = 3, },
                new Course {CourseID = 4022, Title = "Microeconomics", Credits = 3, },
                new Course {CourseID = 4041, Title = "Macroeconomics", Credits = 3, },
                new Course {CourseID = 1045, Title = "Calculus",       Credits = 4, },
                new Course {CourseID = 3141, Title = "Trigonometry",   Credits = 4, },
                new Course {CourseID = 2021, Title = "Composition",    Credits = 3, },
                new Course {CourseID = 2042, Title = "Literature",     Credits = 4, }
            };
         courses.ForEach(s => context.Courses.AddOrUpdate(p => p.Title, s));
         context.SaveChanges();

         var enrollments = new List<Enrollment>
            {
                new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Alexander").StudentID, 
                    CourseID = courses.Single(c => c.Title == "Chemistry" ).CourseID, 
                    Grade = Grade.A 
                },
                 new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Alexander").StudentID,
                    CourseID = courses.Single(c => c.Title == "Microeconomics" ).CourseID, 
                    Grade = Grade.C 
                 },                            
                 new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Alexander").StudentID,
                    CourseID = courses.Single(c => c.Title == "Macroeconomics" ).CourseID, 
                    Grade = Grade.B
                 },
                 new Enrollment { 
                     StudentID = students.Single(s => s.LastName == "Alonso").StudentID,
                    CourseID = courses.Single(c => c.Title == "Calculus" ).CourseID, 
                    Grade = Grade.B 
                 },
                 new Enrollment { 
                     StudentID = students.Single(s => s.LastName == "Alonso").StudentID,
                    CourseID = courses.Single(c => c.Title == "Trigonometry" ).CourseID, 
                    Grade = Grade.B 
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Alonso").StudentID,
                    CourseID = courses.Single(c => c.Title == "Composition" ).CourseID, 
                    Grade = Grade.B 
                 },
                 new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Anand").StudentID,
                    CourseID = courses.Single(c => c.Title == "Chemistry" ).CourseID
                 },
                 new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Anand").StudentID,
                    CourseID = courses.Single(c => c.Title == "Microeconomics").CourseID,
                    Grade = Grade.B         
                 },
                new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Barzdukas").StudentID,
                    CourseID = courses.Single(c => c.Title == "Chemistry").CourseID,
                    Grade = Grade.B         
                 },
                 new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Li").StudentID,
                    CourseID = courses.Single(c => c.Title == "Composition").CourseID,
                    Grade = Grade.B         
                 },
                 new Enrollment { 
                    StudentID = students.Single(s => s.LastName == "Justice").StudentID,
                    CourseID = courses.Single(c => c.Title == "Literature").CourseID,
                    Grade = Grade.B         
                 }
            };

         foreach (Enrollment e in enrollments)
         {
            var enrollmentInDataBase = context.Enrollments.Where(
                s =>
                     s.Student.StudentID == e.StudentID &&
                     s.Course.CourseID == e.CourseID).SingleOrDefault();
            if (enrollmentInDataBase == null)
            {
               context.Enrollments.Add(e);
            }
         }
         context.SaveChanges();
      }
   }
}

      Seed方法使用数据库context对象作为输入参数，使用这个对象把新的实体插入到数据库中。每一个实体类型，代码都创建了一个新的实体集合，把它们添加到相应的DbSet属性中，然后保存到数据库中。
      AddOrUpdate方法，第一个参数用来检查一个行是否已经存在，第二个参数是插入的值。

      Enrollment实体并没有使用AddOrUpdate方法，而是使用循环遍历Enrollment集合，判断是不是已经存在。

（3）add-migration InitialCreate

（4）update-database

      运行Up方法创建数据库，并运行Seed方法填充数据库。

三、创建Student控制器和视图

1.创建Student控制器，选择自动生成控制器代码和视图。

**Conventions

• 实体类名字的复数，被用作数据库表名
• 实体属性的名字，被用作列名
• Id或ClassnameID属性，被标识为主键。

2.创建Details页面

      在EnrollmentDate后面，<fieldset>之前，添加显示注册信息列表的代码。

    <div class="display-label">
        @Html.LabelFor(model => model.Enrollments)
    </div>
    <div class="display-field">
        <table>
            <tr>
                <th>Course Title</th>
                <th>Grade</th>
            </tr>
            @foreach (var item in Model.Enrollments)
            {
                <tr>
                    <td>
                        @Html.DisplayFor(modelItem => item.Course.Title)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => item.Grade)
                    </td>
                </tr>
            }
        </table>
    </div>
</fieldset>
<p>
    @Html.ActionLink("Edit", "Edit", new { id=Model.StudentID }) |
    @Html.ActionLink("Back to List", "Index")
</p>

3.更新Create页面

       更新HttpPost Create方法，添加try-catch和Bind attribute

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(
   [Bind(Include = "LastName, FirstMidName, EnrollmentDate")]
   Student student)
{
   try
   {
      if (ModelState.IsValid)
      {
         db.Students.Add(student);
         db.SaveChanges();
         return RedirectToAction("Index");
      }
   }
   catch (DataException /* dex */)
   {
      //Log the error (uncomment dex variable name after DataException and add a line here to write a log.
      ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
   }
   return View(student);
}

     这段代码使用模型绑定添加Student实体，并保存至数据库。

     ValidateAntiForgeryToken属性，帮助伪造响应跨站攻击。需要在Create视图中，表单里面添加语句“@Html.AntiForgeryToken()”。

     Bind属性用来保护过度提交。例如，假设Student实体包含一个Secret属性，你不想通过网页更新。Exclude参数阻止你希望排除的黑名单字段。

   public class Student
   {
      public int StudentID { get; set; }
      public string LastName { get; set; }
      public string FirstMidName { get; set; }
      public DateTime EnrollmentDate { get; set; }
      public string Secret { get; set; }

      public virtual ICollection<Enrollment> Enrollments { get; set; }
   }

4.更新HttpPost Edit方法

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(
   [Bind(Include = "StudentID, LastName, FirstMidName, EnrollmentDate")]
   Student student)
{
   try
   {
      if (ModelState.IsValid)
      {
         db.Entry(student).State = EntityState.Modified;
         db.SaveChanges();
         return RedirectToAction("Index");
      }
   }
   catch (DataException /* dex */)
   {
      //Log the error (uncomment dex variable name after DataException and add a line here to write a log.
      ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
   }
   return View(student);
}

      Entity状态有Added、Unchanged、Modified、Delete、Detached。
5.更新Delete页面

public ActionResult Delete(bool? saveChangesError=false, int id = 0)
{
    if (saveChangesError.GetValueOrDefault())
    {
        ViewBag.ErrorMessage = "Delete failed. Try again, and if the problem persists see your system administrator.";
    }
    Student student = db.Students.Find(id);
    if (student == null)
    {
        return HttpNotFound();
    }
    return View(student);
}

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Delete(int id)
{
    try
    {
        Student student = db.Students.Find(id);
        db.Students.Remove(student);
        db.SaveChanges();
    }
    catch (DataException/* dex */)
    {
        // uncomment dex and log error. 
        return RedirectToAction("Delete", new { id = id, saveChangesError = true });
    }
    return RedirectToAction("Index");
}

      在ViewsStudentDelete.cshtml页面中，添加错误消息。

<h2>Delete</h2>
<p class="error">@ViewBag.ErrorMessage</p>
<h3>Are you sure you want to delete this?</h3>